A device installed in a movable body such as a vehicle and displaying time should desirably display the correct standard time of the time zone of its current position, even when the self-device moves between time zones with different standard times. As a device for detecting such crossing of a time zone boundary and correcting the displayed time, a conventional time display control device has been known (Japanese Patent Application Publication No. 2010-127808) in which the current position of the self-device is detected on the basis of a GPS (Global Positioning System) signal, for example, whether or not the self-device has crossed a time zone boundary is determined by referring to map information including time zone information, and if the device crosses the time zone boundary, time information held in the self-device is corrected and displayed. Furthermore, to prevent too frequent changes in the displayed time and bothering the driver when driving on a road that frequently crosses a time zone boundary, the device sets an area at a predetermined distance from the time zone boundary, and changes the displayed time only when the vehicle goes beyond the predetermined distance-area toward the destination time zone.
However, the position of the self-device located by the GPS signal generally includes an error, and due to this error, it may sometimes be difficult to accurately detect whether or not the vehicle has crossed a time zone boundary. To improve the accuracy in locating the current position of the self-device, in the field of navigation systems, for example, a method has been known in which the position of the device is calculated by use of a GPS signal, and the calculated position is matched with a road position on a map stored in the self-device (so-called map matching).
However, generally, map information stored in an onboard device such as an onboard navigation system is rarely updated, and if the map information is updated only at the time of a vehicle inspection, there may be a certain period when the device uses map information that does not include latest information such as newly constructed roads. Accordingly, since onboard devices such as an onboard navigation system do not use latest map information, errors may occur in position location by map matching.
As a result, even if the displayed time is kept unchanged within a predetermined distance from a time zone boundary as in the conventional device described above, an error in current position location accuracy may cause frequent changes in the displayed time, depending on the value of the predetermined distance. Additionally, if the area of the predetermined distance is enlarged to avoid such frequent changes in the displayed time, the time may be displayed incorrectly over a needlessly wide area, and usefulness of the time information display device may be degraded.
Meanwhile, in recent years, some multifunction mobile terminals such as a smartphone have a GPS function or a map matching function to locate the position of the self-device and perform navigation, or determine the time zone of the current position of the self-device to correct and display time information. Such a mobile terminal communicates with a server, for example, through radio communication or the like, and can always access latest map information. However, since such a mobile terminal cannot include a large high-performance device in view of balance with required lightness, for example, generally, location accuracy of the GPS function tends to be lower than an onboard GPS device.
For this reason, in a multifunction mobile terminal, a GPS position calculation error may cause an error in position location by map matching. This may cause fluctuation in displayed time near the time zone boundary, in a manner different from the aforementioned onboard device whose map information may cause an error in position location.